The present invention relates generally to an improved train brake system and more specifically to an electropneumatic brake system for integral trains.
An integral train is a train on which the motive power and carrying units are integrated into a single unit, with systems shared between subunits. It is distinct from a conventional train in that it does not require that motive power be utilized into a separable locomotive, and that carrying parts of the train are not required to be switchable in freight yards nor to be capable of exchange between trains. One example of an integral train is the Iron Highway--a train consisting of one or more elements. Each element composed of integrated power and carrying platforms with a control cab at each end of the element. Each element consists of one or two power cabs and a fixed number of platforms. The platforms and power cabs are articulated together in order to both reduce the normal slack between the cars and provide a continuous flat deck over the length of the continuous platform. The reduction of the slack results in a corresponding reduction in the dynamic forces which the cars are required to withstand during the run in and out of the train slack. The reduction of the dynamic forces and elimination of switchyard impacts allows for the use of lighter cars, which allows for an increase in the cargo weight for a given overall train weight and therefore an increase in train efficiency. Additional improvements in efficiency are obtained through the truck design and from other sources.
An example of an integral train is described in my prior U.S. Pat. No. 4,702,291. Because of this unique design of integral trains, there exists an opportunity to design a brake control system without the limitation of standard freight brakes. The system should include the ability to control the brakes throughout the integral train, provide control of a retarder for the propulsion transmission, operate on the parking brakes as well as provide the appropriate operation during an emergency towing by a conventional locomotive.
One example of a computerized brake control system is U.S. Pat. No. 4,402,047 to Newton et at. This is an electropneumatic system which uses transducers and a feedback loop to control the brakes of a single vehicle which in this case is generally the locomotive of a conventional train. The controller of this system uses pressure signal feedbacks to the computer which compares these to a target and makes fine corrections to an output device to provide variations of the signal to maintain the appropriate brake pressure in a brake cylinder. Other examples of electropneumatic brake systems and electrically assisted application and release for fluid pressure brake systems, for example, U.S. Pat. Nos. 4,052,110 and 4,076,322.
Thus, it is an object of the present invention to provide an improved brake control system for integral trains.
It is another object of the present invention to provide an electropneumatic brake control system which will control the brakepipe and parking brakes.
It is another object of the present invention to provide an electropneumatic control system which will permit simultaneous brakepipe reduction and restoration at a number of points along a train.
It is a further object of the present invention to provide a brake control system which controls the brakepipe, a parking brake and a propulsion transmission retarder.
A still further object of the present invention is to provide a brake control system which can be used with a conventional locomotive during an emergency tow.
These and other objects are achieved by a system including a control valve for controlling pressure on the brakepipe in response to a brake control signal, a cut-off valve connecting the control valve to the brakepipe and a converter for converting digital values of electric brake signals to discreet pneumatic brake control signals for the control valve. A controller provides the digital electric brake signals for controlling brakepipe pressure. The converter valve is a pilot valve having a plurality of solenoids responsive to the digital values. This allows accurate repeatable control and produces the discreet pneumatic brake control signals. The unique converter, in response to digital signals, allows the appropriate control of the brakepipe pressure without the need for any electronic feedback signals. The control valve includes a first pressure sensitive element responsive to a first pressure signal to maintain the brakepipe at a fixed first pressure value and a second pressure responsive element responsive to the pneumatic brake control signal from the converter to reduce pressure in the brakepipe to values which are discreet fractions below the first value. The first pressure sensitive element compares brakepipe to the first pressure signal and the second pressure sensitive element is connected to the first pressure element and reduces the effect of the first pressure signal in response to the pneumatic brake control signal. A feeder valve determines the first pressure signal. The pneumatic brake control signal varies in a range from zero to the first pressure signal and a ratio of the response of the first and second pressure sensitive elements defines the brakepipe service braking pressure range.
For integral trains, the electropneumatic brake control system includes at least two brakepipe control systems, each including a control valve, a cut-off valve, a converter valve and a controller. The second brakepipe control system may include transducers for sensing the first pressure signal provided to its control valve as a reference and the brakepipe pressure. The controller of the second system, and further systems on the common brakepipe which are the trailing or slave systems, doses its cut-off valve at a difference between the measured first pressure signal and measured brakepipe pressure. This prevents the second brakepipe control system from attempting to charge the brakepipe while the lead or master or first brakepipe control system is attempting to reduce the pressure in the brakepipe control system.
Each system includes an electropneumatic emergency vent valve connected to the brakepipe and the controller controls the cut-off valve to close and controls the electropneumatic emergency vent valve to open for an emergency braking. Also, a pneumatic emergency vent valve is connected in response to an emergency brakepipe pressure in the brakepipe to vent the brakepipe. A transducer senses an emergency brakepipe pressure in the brakepipe and the controller controls the cut-off valve and the electropneumatic emergency vent valve in response to an emergency input from the transducer or an emergency input from an operator.
This system also includes a pneumatic parking brake system responsive to brakepipe pressure for applying and releasing a parking brake so that parking brake will be automatically released by a towing locomotive, but not be applied at any time by the controller as during normal operation. An electropneumatic parking brake valve is connected to the parking brake by the pneumatic parking brake valve and is controlled by the controller to apply and release the parking brake. The system includes a retarder valve connected to a retarder control actuator on powered platforms. The controller controls the retarder valve to provide pneumatic retard signals to operate the retarder actuator to achieve dynamic braking. An interlock valve, in the pneumatic circuit of the brake cylinder, is responsive to file retarder control pipe signals to reduce the brake cylinder pressure when the wheels associated with a particular brake cylinder are being braked by the retarder. This prevents over braking and wheel slip.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.